This invention relates generally to the manufacture of semi-conductor discs or wafers, and specifically, to methods of and apparatus for transfer of a plurality of said discs to and from a slab-form quartz boat or its equivalent during various stages of the manufacturing process.
Slotted carriers have been widely used in the electronics manufacturing arts for transferring a plurality of semi-conductor discs to and from quartz boats during various stages of the manufacturing process. For example, discs may be placed in the carrier during an ancillary stage of their manufacturing process, e.g. an acid bath, and then transferred to a quartz boat for a different stage of the process, e.g. an epitaxial reaction. Two basic methods have been widely used for transferring the discs from the carrier to the boat. The first method entails positioning the boat over an open top of the carrier, and the inverting the carrier so that the discs fall from the carrier into the slots in the quartz boats. However, in this method a quartz cassette form boat or basket carrier is employed having either a trapezoidal or triangular cross-sectional configuration formed by either four or three parallel rails, the rail having grooves or slots to receive the edges of the discs. A second method is to transfer the discs individually by means of tweezers from the carrier to the boat by lifting each disc from the carrier and depositing it in an appropriate slot in the boat. This method is intolerably slow.
Indigenous to the two aforementioned methods of transfer is the damage that occurs to the discs. The impact, known as "clicking," which the edges of the discs receive in the conventional dump transfer technique tends to damage the circuits on the discs both by chipping of the edges and by damage to circuits on the discs from the shock of "clicking." It has been found in the industry that as many as four of the electronic circuits applied to the discs can be irreparably damaged with each "clicking," and the expense incurred in this damage has proven to be significant. The use of tweezers can also damage circuits at the point of tweezer contact. It will be recognized by those skilled in the art that it is desirable to minimize the expensive damage to the discs by minimizing "clicking" and tweezer contact while not increasing the time required for transfer. Yet, for over a decade no mechanically feasible means of transferring the discs has been devised which would not seriously and deleteriously affect efficiency of the manufacturing process.